Heat Transfer Performance of Double Tube Hairpin Heat
Exchager by Using Cfd Analysis with Mgo Nano Fluidat
Different Volume Fractions
Dr. P. Srinivasulu , Mr.B.Nagaraju , Sayyad Shabana
1 Professor And Hod, 2assistant Professor, 3m.Tech (Thermal Engineering) Student
Dept. Of Mechanical Engineering, "Vaagdevi College Of Engineering" Bollikunta, Warangal, Telangana 506005.
Heat exchanger is a device used to transfer heat between one or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. In this thesis, MgO nano fluid is mixed with base fluid water is analyzed for their performance in the hair pin heat exchanger. The nano fluid MgO is mixed with water at different volume fractions (0.000625, 0.00125, 0.0025, 0.005 and 0.01). Theoretical calculations are done determine the properties for nano fluids and those properties are used as inputs for analysis.
3D model of the hair pin heat exchanger is done in CREO parametric software. CFD analysis is done on the hair pin heat exchanger with MgO nano fluid at different volume fractions and thermal analysis is done in ANSYS for two materials Aluminum7085 and Copper.
Keywords: Finite element analysis, Hair pin heat exchanger, CFD analysis, thermal analysis.
Heat exchangers are one of the mostly used equipment in the process industries. Heat Exchangers are used to transfer heat between two process streams. One can realize their usage that any process which involve cooling, heating, condensation, boiling or evaporation will require a heat exchanger for these purpose. Process fluids, usually are heated or cooled before the process or undergo a phase change. Different heat exchangers are named according to their application. For example, heat exchangers being used to condense is known as condensers, similarly heat exchanger for boiling purposes are called boilers. Performance and efficiency of heat exchangers are measured through the amount of heat transfer using least area of heat transfer and pressure drop. A better presentation of its efficiency is done by calculating over all heat transfer coefficient.
Pressure drop and area required for a certain amount of heat transfer, provides an insight about the capital cost and power requirements (Running cost) of a heat exchanger. Usually, there is lots of literature and theories to design a heat exchanger according to the requirements.
DESIGN AND ANAYSIS OF DOUBLE PIPE HEAT
EXCHANGER USING COMPUTATIONAL
III. INTRODUCTION TO CAD
Computer-aided design (CAD) is the use of computer systems (or workstations) to aid in the creation, modification, analysis, or optimization of a design. CAD software is used to increase the productivity of the designer, improve the quality of design, improve communications through documentation, and to create a database for manufacturing. CAD output is often in the form of electronic files for print, machining, or other manufacturing operations. The term CADD (for Computer Aided Design and Drafting) is also used.
INTRODUCTION TO CREO
CREO, formerly known as Pro/ENGINEER, is 3D modeling software used in mechanical engineering, design, manufacturing, and in CAD drafting service firms. It was one of the first 3D CAD modeling applications that used a rule-based parametric system. Using parameters, dimensions and features to capture the behavior of the product, it can optimize the development product as well as the design itself.
Dimensions of designed double tube Hair-pin heat exchanger:
Outer pipe specification Inner tube specification
Copper tube of U bends I.D. of shell= 19.05 mm I.D. of tube = 8.4 mm Copper tube of U bends I.D. of shell= 19.05 mm I.D. of tube = 8.4 mm
O.D. of shell = 22 mm O.D. of tube = 9.5 mm Center to center distance is taken
Wall thickness= 0.55 mm 127
1.5 - 1.8 times of outer dia. of shell. Thermal conductivity of wall= 385 w/m2K Length of each G.I. pipe =
Effective length of copper tube through which heat transfer could take place= 45cm
Total length of the copper tube = straight part (51cm) + U-shaped bend part (9cm) =60cm
3D model of hair pin heat exchanger
IV. INTRODUCTION TO FINITE ELEMENT METHOD
FEM/FEA helps in evaluating complicated structures in a system during the planning stage. The strength and design of the model can be improved with the help of computers and FEA which justifies the cost of the analysis. FEA has prominently increased the design of the structures that were built many years ago.
INTRODUCTION TO CFD
Computational fluid dynamics, usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows.
CALCULATIONS TO DETERMINE PROPERTIES OF NANO FLUID BY CHANGING VOLUME FRACTIONS
NANO FLUID CALCULATIONS NOMENCLATURE
ρnf = Density of nano fluid (kg/m3)
ρs = Density of solid material (kg/m3)
ρw = Density of fluid material (water) (kg/m3)
ϕ = Volume fraction
Cpw = Specific heat of fluid material (water) (j/kg-k)
Cps = Specific heat of solid material (j/kg-k)
µw = Viscosity of fluid (water) (kg/m-s)
µ = Viscosity of Nano fluid
Kw = Thermal conductivity of fluid material (water) (W/m-k)
Ks = Thermal conductivity of solid material (W/m-k)
DENSITY OF NANO FLUID
ρnf = ϕ×ρs + [(1-ϕ) × ρw]
SPECIFIC HEAT OF NANO FLUID
Cp nf = ϕ×ρs×ϕCps×ρs+ +(11−−ϕϕ ()×ρwρw×Cpw)
VISCOSITY OF NANO FLUID
µnf =µw (1+2.5ϕ)
THERMAL CONDUCTIVITY OF NANO FLUID
Knf = KsKs++2Kw2Kw+−22KsKs−−KwKw 11++ββ³³××ϕϕ × kw
CFD ANALYSIS OF HAIR PIN HEAT EXCHANGER
MAGNESIUM OXIDE NANO FLUID
VOLUME FRACTION - 0.01
HEAT TRANSFER CO-EFFICIENT
MASS FLOW RATE
HEAT TRANSFER RATE
THERMAL ANALYSIS OF HAIR PIN HEAT EXCHANGER
THERMAL ANALYSIS OF HAIR PIN HEAT EXCHANGER
CFD RESULT TABLES
THERMAL ANALSIS RESULTS TABLES
CFD ANALYSIS GRAPHS
HEAT TRANSFER COEFFICIENT PLOT
HEAT TRANSFER RATE PLOT
THERMAL ANALYSIS GRAPHS
In this thesis, MgO nano fluid is mixed with base fluid water are analyzed for their performance in the hair pin heat exchanger. The nano fluid is magnesium Oxide for FIVE volume fractions 0.000625, 0.00125, 0.0025, 0.005 & 0.01. Theoretical calculations are done determine the properties for nano fluids and those properties are used as inputs for analysis. Hairpin Exchangers are available in single tube (Double Pipe) or multiple tubes within a hairpin shell (Multitude), bare tubes, finned tubes, U-tubes, straight tubes (with rod-thru capability), fixed tube sheets and removable bundle.
By observing the CFD analysis results the heat transfer rate value more at magnesium oxide volume fraction 0.01.
By observing the thermal analysis results the heat flux value more for copper material compare with aluminum alloy7085.
So it can be concluded the magnesium oxide nano fluid at volume fraction 0.01 fluid is the better fluid for hair pin heat exchanger and material is copper.
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